This invention relates to a superconducting wire containing a multifilamentary superconducting alloy.
A multifilamentary Nb-Ti alloy superconducting wire made by distributing a multiplicity of Nb-Ti alloy filaments through a matrix comprising Cu or a Cu-Ni alloy is disclosed in, for example, "Multifilamentary Superconducting Composites" (CRYOGENICS, pp. 3-10, Feb. 1971, P.R. Critchlow et al.), as one type of the superconducting wire containing a multifilamentary superconducting alloy.
Such multifilamentary Nb-Ti alloy superconducting wire, as shown in FIG. 3 in cross sections, has a structure in which a plurality of Nb-Ti alloy filaments 1 are distributed through a matrix 2, forming a structure of composite as a whole. In this structure, Cu or a Cu-Ni alloy is used as the material for the matrix 2.
Such multifilamentary Nb-Ti alloy superconducting wire is manufactured by drilling a plurality of holes through a rod comprising a matrix material and inserting rods comprising a Nb-Ti alloy into the holes, followed by drawing of the entire rod composite under heating to allow it to have a smaller diameter, and repeating the above drawing operation using the resulting rod composite to allow it to have smaller diameter step by step, such that the rods contained in the rod may be finally formed into thin filaments.
In the above conventional method, however, there is a problem that a filament having a high critical current density cannot be obtained because the core material of Nb-Ti alloy and the the matrix of Cu or Cu-Ni alloy are brought into direct contact with each other which are drawn under heating in such state, so that in this process, an intermetallic compound shown by "Cu.sub.x Ti.sub.y " ("x" and "y" each represent an index showing the number of reacted mole number) is formed along the interface between the core material and the matrix, causing constrictions in the resulting Nb-Ti alloy filament or disconnections in the filament during the drawing process.
moreover, if the formation of "Cu.sub.x Ti.sub.y " along the interface between the core material of Nb-Ti alloy and the matrix is intended to be inhibited by using a reduced number of hot wire drawing to be repeated, in order to obviate the above problem, there is another problem that a wire having a large current capacity can hardly be obtained since the number of the Nb-Ti alloy filaments is restricted as the result of the failure in reducing the diameter of the filaments, and thus the Nb-Ti alloy filaments come to have a low critical current density.
This problem is commonly found in such cases where the intermetallic compound is formed between the core material of superconducting alloy and the matrix in which the core material is distributed, cuasing constriction or disconnection in the filaments during the process of drawing, when superconducting wires are generally made by burying a core material of superconducting alloy in a matrix.